Organic light emitting display

ABSTRACT

An organic light emitting display is disclosed. In one embodiment, the display includes 1) a substrate, 2) a plurality of pixels formed on the substrate, wherein each of the pixels comprises at least one circuit region including i) a first light emission area, ii) a second light emission area iii) at least one transmission area transmitting external light, and iv) a pixel circuit unit and 3) a first pixel electrode formed in the first light emission area and electrically connected to the pixel circuit unit, wherein the first pixel electrode comprises a first transparent conductive layer and a reflective layer. The display may further include 1) a second pixel electrode formed in the second light emission area and electrically connected to the first pixel electrode, wherein the second pixel electrode comprises a second transparent conductive layer, 2) a first opposite electrode substantially directly below or above the first pixel electrode, 3) a second opposite electrode substantially directly below or above the second pixel electrode and 4) an organic emission layer formed between the first pixel electrode and the first opposite electrode and between the second pixel electrode and the second opposite electrode.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/176,293, filed on Jul. 5, 2011, which claims the benefit of KoreanPatent Application No. 10-2010-0092854, filed on Sep. 24, 2010, in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

1. Field

The described technology generally relates to an organic light emittingdisplay, and more particularly, to a transparent organic light emittingdisplay.

2. Description of the Related Technology

Organic light emitting displays generally have wide viewing angles, highcontrast ratios, short response times, and reduced power consumption.The displays may be used across a variety of applications such aspersonal portable devices (e.g., MP3 players and mobile phones) or alarge screen display (e.g., television sets). An organic light emittingdisplay is self-emissive. Also, the weight and thickness of the organicdisplay can be reduced since it does not require an additional lightsource unlike a liquid crystal display. Further, the device can be madetransparent by using transparent thin film transistors and othertransparent elements (e.g., transparent organic light emittingelements).

SUMMARY

One aspect is an organic light emitting display that is transparent byimproving a light transmittance at a transmission region and may beformed as a dual-emission type.

Another aspect is a transparent organic light emitting display thatprevents distortion of images by restraining scatter of transmittedlight.

Another aspect is an organic light emitting display including: asubstrate; a plurality of pixels formed on the substrate, and eachcomprising at least one circuit area including a first emission area anda second emission area emitting light, at least one transmission areatransmitting external light, and a pixel circuit unit; a plurality offirst pixel electrodes disposed on the first emission areas of thepixels, electrically connected to the pixel circuit units, andcomprising transparent conductive layers and reflective layers; aplurality of second pixel electrodes disposed on the second emissionareas, electrically connected to the first pixel electrodes, andcomprising transparent conductive layers; a first opposite electrodefacing the first pixel electrode; a second opposite electrode facing thesecond pixel electrode; and organic layers disposed between the firstpixel electrode and the first opposite electrode and between the secondpixel electrode and the second opposite electrode, and comprisingemission layers.

At least a part of the second emission area may be disposed on thetransmission area. The first pixel electrode and the second pixelelectrode may be connected to each other. The transparent conductivelayer may be formed of at least one metal oxide selected from the groupconsisting of indium tin oxide (ITO), indium zinc oxide (IZO), ZnO, andIn₂O₃.

The second pixel electrode may further include a reflective layer thatis formed to reflect or transmit the light. The reflective layer mayinclude at least one metal material selected from the group consistingof Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Yb, and an alloythereof. The first opposite electrode and the second opposite electrodemay be integrally formed with each other.

The first opposite electrode may be formed to transmit the light. Thesecond opposite electrode may be formed to reflect the light. The firstopposite electrode and the second opposite electrode may include atleast one metal selected from the group consisting of Ag, Mg, Al, Pt,Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Yb, and an alloy thereof.

Another aspect is an organic light emitting display including: asubstrate; a plurality of pixels formed on the substrate, and eachcomprising at least one circuit area including a first emission area anda second emission area emitting light, at least one transmission areatransmitting external light, and a pixel circuit unit, wherein at leasta part of the second emission area is disposed on the transmission area;a plurality of transmission windows formed in the at least onetransmission area; a plurality of first pixel electrodes disposed on thefirst emission areas of the pixels, electrically connected to the pixelcircuit units, and comprising transparent conductive layers andreflective layers; a plurality of second pixel electrodes disposed onthe second emission areas, electrically connected to the first pixelelectrodes, and comprising transparent conductive layers; a firstopposite electrode facing the first pixel electrode; a second oppositeelectrode facing the second pixel electrode; and organic layers disposedbetween the first pixel electrode and the first opposite electrode andbetween the second pixel electrode and the second opposite electrode,and comprising emission layers.

The first pixel electrode and the second pixel electrode may beconnected to each other. The transparent conductive layer may be formedof at least one metal oxide selected from the group consisting of indiumtin oxide (ITO), indium zinc oxide (IZO), ZnO, and In₂O₃. The secondpixel electrode may further include a reflective layer that is formed toreflect or transmit the light.

The reflective layer may include at least one metal material selectedfrom the group consisting of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li,Ca, Yb, and an alloy thereof. The first opposite electrode and thesecond opposite electrode may be integrally formed with each other. Thefirst opposite electrode may be formed to transmit the light. The secondopposite electrode may be formed to reflect the light. The firstopposite electrode and the second opposite electrode may include atleast one metal selected from the group consisting of Ag, Mg, Al, Pt,Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Yb, and an alloy thereof.

Another aspect is an organic light emitting display comprising: asubstrate; a plurality of pixels formed on the substrate, wherein eachof the pixels comprises at least one circuit region including i) a firstlight emission area, ii) a second light emission area iii) at least onetransmission area transmitting external light, and iv) a pixel circuitunit; a first pixel electrode formed in the first light emission areaand electrically connected to the pixel circuit unit, wherein the firstpixel electrode comprises a first transparent conductive layer and areflective layer; a second pixel electrode formed in the second lightemission area and electrically connected to the first pixel electrode,wherein the second pixel electrode comprises a second transparentconductive layer; a first opposite electrode substantially directlybelow or above the first pixel electrode; a second opposite electrodesubstantially directly below or above the second pixel electrode; and anorganic emission layer formed between the first pixel electrode and thefirst opposite electrode and between the second pixel electrode and thesecond opposite electrode.

In the above display, at least part of the second light emission areaoverlaps with the transmission area. In the above display, the first andsecond pixel electrodes are connected to each other and formed on theorganic layer. In the above display, at least one of the first andsecond transparent conductive layers is formed of at least one metaloxide selected from the group consisting of indium tin oxide (ITO),indium zinc oxide (IZO), ZnO, and In₂O₃. In the above display, thesecond pixel electrode is partially transmissive and partiallyreflective.

In the above display, the reflective layer of the first pixel electrodecomprises at least one metal material selected from the group consistingof Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Yb, and an alloythereof. In the above display, the first and second opposite electrodesare integrally formed with each other. In the above display, the firstopposite electrode is at least partially transmissive. In the abovedisplay, the second opposite electrode is at least partially reflective.In the above display, at least one of the first and second oppositeelectrodes comprises at least one metal selected from the groupconsisting of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Yb, and analloy thereof.

Another aspect is an organic light emitting display comprising: asubstrate; a plurality of pixels formed on the substrate, wherein eachof the pixels comprises at least one circuit region including i) a firstlight emission area, ii) a second light emission area, iii) at least onelight transmission area, and iv) a pixel circuit unit, and wherein atleast part of the second emission area overlaps with the lighttransmission area; at least one transmission window formed in the lighttransmission area; a first pixel electrode formed on the first lightemission area and electrically connected to the pixel circuit unit,wherein the first pixel electrode is at least partially reflective; asecond pixel electrode formed on the second light emission area andelectrically connected to the first pixel electrode, wherein the secondpixel electrode is at least partially transmissive; a first oppositeelectrode substantially directly below or above the first pixelelectrode; a second opposite electrode substantially directly below orabove the second pixel electrode; and an organic emission layer formedbetween the first pixel electrode and the first opposite electrode andbetween the second pixel electrode and the second opposite electrode.

In the above display, the first and second pixel electrodes contact eachother and formed on the organic layer. In the above display, the firstpixel electrode is thicker than the second pixel electrode. In the abovedisplay, the second pixel electrode is formed of a partiallytransmissive material and a partially reflective material. In the abovedisplay, the pixel circuit unit is formed substantially directly belowor above the first pixel electrode and is not formed in the lighttransmission area.

In the above display, the second pixel electrode is closer to the lighttransmission area than the first pixel electrode. The above displayfurther comprises at least one insulating layer contacting the pixelcircuit unit, wherein the at least one transmission window contacts theinsulating layer. In the above display, the at least one transmissionwindow comprises a first transmission window formed on a pixel defininglayer. In the above display, the at least one transmission windowcomprises a second transmission window formed on a passivation layer andformed between the first and second pixel electrodes.

Another aspect is an organic light emitting display comprising: asubstrate; a plurality of pixels formed on the substrate, wherein eachof the pixels comprises i) a first light emission area, ii) a secondlight emission area, iii) a light transmission area and iv) at least onecircuit element which is formed substantially directly below or abovethe first light emission area and is not formed in the lighttransmission area, and wherein the second light emission area at leastpartially overlaps with the light transmission area; a first pixelelectrode formed on the first light emission area and electricallyconnected to the circuit element, wherein the first pixel electrode isat least partially reflective; a second pixel electrode formed on thesecond light emission area and electrically connected to the first pixelelectrode, wherein the second pixel electrode is at least partiallytransmissive; and an organic light emitting diode contacting and formedover the first and second pixel electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an organic light emitting displayaccording to an embodiment.

FIG. 2 is a cross-sectional view of an organic light emitting displayaccording to another embodiment.

FIG. 3 is a schematic diagram of an organic emission unit shown in FIG.1 or FIG. 2.

FIG. 4 is a schematic diagram of the organic emission unit illustratinga pixel circuit unit of FIG. 3 in detail.

FIG. 5 is a detailed plan view of the organic emission unit of FIG. 4.

FIG. 6 is a cross-sectional view of the organic emission unit takenalong line A-A of FIG. 5.

FIG. 7A is a cross-sectional view showing an example of a first emissionarea (PA1) of FIG. 6.

FIG. 7B is a cross-sectional view showing an example of a secondemission area (PA2) of FIG. 6.

FIG. 8 is a cross-sectional view of an organic emission unit accordingto another example.

FIG. 9 is a cross-sectional view of an organic emission unit accordingto another example.

FIG. 10A is a cross-sectional view of a first emission area (PA1) ofFIG. 9.

FIG. 10B is a cross-sectional view of a second emission area (PA2) ofFIG. 9.

FIG. 11 is a plan view of an organic emission unit according to anotherexample.

DETAILED DESCRIPTION

A transparent display, when in an off state, generally allows an object,positioned on an opposite side of a user with respect to the display, tobe transmitted to the user. This transmission may occur not only throughorganic light emitting diodes but also through spaces between patternsof thin film transistors and various wires. However, the lighttransmittance of a transparent organic light-emitting display is notvery high, because the light transmittance of display components such astransistors and various wires are low, and there is little space betweenthe wires.

In addition, a distorted image may be transmitted to the user due to thepatterns. This is because gaps between the patterns are only a fewnanometers, a dimension which is close to the wavelengths of visiblelight, and thus, light scatters while passing through the gaps.

Meanwhile, organic light emitting displays may be realized as adual-emission type display when compared with LCDs. However, in thedual-emission type display, a reflective anode may not be used, andthus, an optical resonant effect may not be obtained. Accordingly,greater light extracting efficiency may not be obtained.

Hereinafter, embodiments will be described in detail with reference toaccompanying drawings. FIG. 1 is a cross-sectional view of an organiclight emitting display 1 according to an embodiment.

Referring to FIG. 1, the organic light emitting display 2 includes anorganic emission unit 21 formed on a first surface 11 of a substrate 1,and a sealing substrate 23 for sealing the organic emission unit 21.

The sealing substrate 23 may be formed at least partially of atransparent material so that images emitted from the unit 21 may bedisplayed therethrough, and substantially prevents external air andmoisture from infiltrating into the organic emission unit 21.

Edges of the substrate 1 and the sealing substrate 23 are coupled toeach other by a sealing material (e.g., frit) 24 so as to substantiallyseal the space 25 between the substrate 1 and the sealing substrate 23.An absorbent or a filler may be provided in the space 25.

As shown in FIG. 2, instead of using the sealing substrate 23, a thinsealing film 26 may be formed on the organic emission unit 21 so as toprotect the organic element 21 from external impurities such as air ormoisture. The sealing film 26 may include an alternately stackedstructure of i) an inorganic film formed at least partially of, forexample, silicon oxide or silicon nitride and ii) an organic film formedat least partially of, for example, epoxy or polyimide. However, thesealing film 26 may have other sealing structure including a transparentfilm.

FIGS. 3 and 4 are plan views showing a red pixel P_(r), a green pixelP_(g), or a blue pixel P_(b) that are adjacent to each other in theorganic emission unit 21. FIG. 4 is a detailed schematic diagram showinga pixel circuit unit PC of FIG. 3.

Each of the red, green, and blue pixels P_(r), P_(g), and P_(b) has afirst emission area PA1, a second emission area PA2, and a transmissionarea TA. The transmission area TA may be separately provided in each ofthe pixels P_(r), P_(g), and P_(b), or may be shared by the pixelsP_(r), P_(g), and P_(b).

Referring to FIGS. 1 through 4, the organic emission unit 21 is formedon the substrate 1 that is divided into i) the transmission areas TA,and ii) the plurality of first emission areas PA1 that are separated bythe transmission areas TA (see FIGS. 3 and 4). The plurality of secondemission areas PA2 that are respectively adjacent to the plurality offirst emission areas PA1 are located on at least part of thetransmission areas TA so that the second emission areas PA2 bothtransmit the external light into the display and emit the light towardthe environment.

As shown in FIG. 4, each of the first emission areas PA1 includes apixel circuit unit PC, and a plurality of conductive lines such as ascan line S, a data line D, and a Vdd line V (driving voltage line) areelectrically connected to the pixel circuit unit PC. Although not shownin FIG. 4, various additional conductive lines may be formed accordingto a structure of the pixel circuit unit PC. In one embodiment, at leastsome of the pixel circuit unit PC and the above conductive lines are notformed directly below or above the second emission areas PA2.

The pixel circuit unit PC includes i) a first thin film transistor TR1electrically connected to the scan line S and the data line D, ii) asecond thin film transistor TR2 electrically connected to the first thinfilm transistor TR1 and the Vdd line V, and iii) a capacitor Cstelectrically connected to the first and second thin film transistors TR1and TR2. In one embodiment, the first thin film transistor TR1 is aswitching transistor and the second thin film transistor TR2 is adriving transistor. The second thin film transistor TR2 is electricallyconnected to a first pixel electrode 221. In one embodiment, as shown inFIG. 4, the first and second thin film transistors TR1 and TR2 areP-type transistors. In another embodiment, at least one of the first andsecond thin film transistors TR1 and TR2 is an N-type transistor. Thenumber of thin film transistors and the number of the capacitor are notlimited to the above example, and two or more thin film transistors andone or more capacitors may be formed according to the configuration ofthe pixel circuit unit PC.

In one embodiment, as shown in FIGS. 3 and 4, the scan lines S, the datalines D, and the Vdd lines V at least partially overlap with the firstpixel electrode 221. In another embodiment, at least one of theconductive lines (e.g., S, D, V) may at least partially overlap with thefirst pixel electrode 221. Depending on the embodiment, all of theconductive lines may be disposed next to the first pixel electrode 221.

In one embodiment, each of the first emission areas PA1 is a topemission type, a light extracting efficiency of which is excellent, ineach of sub-pixels, which will be described later. In addition, sincethe pixel circuit unit PC is located in the top emission area, the usermay see the external portion through the transmission area TA includingthe second emission area PA2. That is, since the conductive patterns ofthe pixel circuit unit PC, which is generally the largest element forreducing the light transmittance of the transmission area TA, are notlocated on the transmission area TA, the light transmittance of thetransmission area TA may be improved.

As described above, according to one embodiment, the organic emissionunit 21 displaying the images is divided into the first emission areaPA1 and the transmission area TA. Further, most conductive patterns thatreduce the entire light transmittance of the display are disposed on thefirst emission area PA1 in order to increase the light transmittance ofthe transmission area TA. Thus, a light transmittance of the entireimage displaying area (the organic emission unit 21 of FIG. 1 or FIG. 2)may be significantly improved compared to a typical transparent displaywhere conductive patterns are formed in both light emission areas andlight transmission area.

Moreover, since the pixel circuit unit PC is disposed to substantiallyoverlap with the first emission area PA1, distortion of external images,which is generated because the external light is scattered due to thepatterns of the devices in the pixel circuit unit PC, may besubstantially prevented.

Although at least one of the conductive lines (e.g., S, D, V) may bedisposed to cross the transmission area TA located between two adjacentfirst emission areas PA1, the conductive lines are very thin, and thus,do not affect the entire light transmittance of the organic emissionunit 21 and are hardly seen by the user. In addition, even if the usermay not see the external image as much as the region blocked by thefirst emission areas PA1, the first emission areas PA1 may be like aplurality of points arranged substantially regularly on the entiredisplay area. Thus, the user can easily see the external images.

The first pixel electrode 221 is disposed on the first emission areaPA1, and the pixel circuit unit PC substantially overlaps with the firstpixel electrode 221 so as to be substantially blocked by the first pixelelectrode 221. In addition, at least one of the conductive lines may bedisposed to cross the first pixel electrode 221. Since the conductivelines may less affect the light transmittance than the pixel circuitunit PC does, the conductive lines may be disposed adjacent to the firstpixel electrode 221 according to the design condition. In oneembodiment, the first pixel electrode 221 includes a reflective layerformed at least partially of a conductive metal reflecting light as willbe described later, and thus, the first pixel electrode 221substantially blocks the pixel circuit unit PC and prevents the externalimages from being distorted by the pixel circuit unit PC on the firstemission area PA1.

A second pixel electrode 222 is further disposed on the transmissionarea TA to form the second emission area PA2. In one embodiment, thesecond pixel electrode 222 is formed at least partially of a metal oxidetransmitting the light so that the second emission area PA2 becomes abottom emission type.

FIG. 5 is a plan view of the organic emission unit 21 showing the pixelcircuit unit PC of FIG. 4 in more detail. FIG. 6 is a cross-sectionalview of the pixel circuit unit PC taken along line A-A of FIG. 5.

In one embodiment, as illustrated in FIGS. 5 and 6, a buffer layer 211is formed on a first surface 11 of the substrate 1, and the first thinfilm transistor TR1, the capacitor Cst, and the second thin filmtransistor TR2 are formed on the buffer layer 211.

First, a first semiconductor active layer 212 a and a secondsemiconductor active layer 212 b are formed on the buffer layer 211.

The buffer layer 211 may be formed of various materials so as to preventinfiltration of impurities and to planarize a surface of the substrate1. For example, the buffer layer 211 may be formed at least partially ofan inorganic material such as silicon oxide, silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, titanium oxide, ortitanium nitride, an organic material such as polyimide, polyester, oracryl, or a stacked substance thereof. Depending on the embodiment, thebuffer layer 211 may be omitted.

The first and second semiconductor active layers 212 a and 212 b may beat least partially formed of polycrystalline silicon. Further, the firstand second semiconductor active layers 212 a and 212 b may be formed atleast partially of an oxide semiconductor. For example, thesemiconductor active layer 212 may be a G-I-Z-O layer[(In₂O₃)a(Ga₂O₃)b(ZnO)c layer] (a, b, c are real numbers satisfyingconditions of a≧0, b≧0, c>0).

A gate insulating layer 213 is formed on the buffer layer 211 so as tocover the first and second semiconductor active layers 212 a and 212 b,and a first gate electrode 214 a and a second gate electrode 214 b areformed on the gate insulating layer 213.

An interlayer dielectric 215 is formed on the gate insulating layer 213so as to cover the first and second gate electrodes 214 a and 214 b. Afirst source electrode 216 a and a first drain electrode 217 a, and asecond source electrode 216 b and a second drain electrode 217 b areformed on the interlayer dielectric 215 so as to contact the first andsecond semiconductor active layers 212 a and 212 b through contactholes.

In FIG. 6, the scan line S may be formed substantially simultaneouslywhen the first and second gate electrodes 214 a and 214 b are formed. Inone embodiment, the data line D is formed substantially simultaneouslywhen the first source electrode 216 a is formed so as to be electricallyconnected to the first source electrode 216 a, and the Vdd line V may beformed substantially simultaneously when the second source electrode 216b is formed so as to be electrically connected to the second sourceelectrode 216 b.

In one embodiment, a lower electrode 220 a of the capacitor Cst isformed substantially simultaneously when the first and second gateelectrodes 214 a and 214 b, and an upper electrode 220 b of thecapacitor Cst is formed substantially simultaneously when the firstdrain electrode 217 a is formed.

The above structure is not considered limiting. For example, the firstand second thin film transistors TR1 and TR2 are formed as top-gatestructures; however, they may be formed as bottom-gate structures, inwhich the first and second gate electrodes 214 a and 214 b are formedrespectively under the first and second semiconductor active layers 212a and 212 b. Other structures of the thin film transistor may be alsoused.

A passivation layer 218 is formed to cover the first thin filmtransistor TR1, the capacitor Cst, and the second thin film transistorTR2. The passivation layer 218 may be a single insulating layer or aplurality of insulating layers having a substantially flat uppersurface. The passivation layer 218 may be formed at least partially of atransparent inorganic insulating material and/or an organic insulatingmaterial.

As shown in FIGS. 5 and 6, the first pixel electrode 221 is formed onthe passivation layer 218 to substantially block the first thin filmtransistor TR1, the capacitor Cst, and the second thin film transistorTR2. The first pixel electrode 221 is electrically connected to thesecond drain electrode 217 b of the second thin film transistor TR2through a via hole formed in the passivation layer 218.

In addition, a second pixel electrode 222 is formed on the passivationlayer 218 to be adjacent to and/or to contact the first pixel electrode221. The first and second pixel electrodes 221 and 222 may beelectrically connected to each other, and the connected body of thefirst and second pixel electrodes 221 and 222 may be formed as an islandthat is independently formed on each of the pixels, as shown in FIG. 5.

A pixel defining layer 219 covers edge portions of the first pixelelectrode 221 and the second pixel electrode 222, and an organic layer223 is formed on the first pixel electrode. In addition, a firstopposite electrode 224 a and a second opposite electrode 224 b areformed to cover the organic layer 223. Therefore, the first oppositeelectrode 224 a is formed on the first emission area PA1 and the secondopposite electrode 224 b is formed on the second emission area PA2. Inone embodiment, at least part of the second opposite electrode 224 b isformed on the transmission area TA.

The organic layer 223 may be formed at least partially of alow-molecular weight organic material or a high-molecular weight organicmaterial. When including a low-molecular weight organic layer, theorganic layer 223 may have a single or multi-layer structure includingat least one selected from the group consisting of a hole injectionlayer (HIL), a hole transport layer (HTL), an emission layer (EML), anelectron transport layer (ETL), and an electron injection layer (EIL).Examples of available organic materials may include copperphthalocyanine (CuPc), N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine(NPB), tris-8-hydroxyquinoline aluminum (Alq3), and the like. Thelow-molecular weight organic layer may be formed by vacuum deposition.Here, the EML is independently formed in each of the red, green, andblue pixels P_(r), P_(g), and P_(b), and the HIL, the HTL, the ETL, andthe EIL are common layers applied commonly to the red, green, and bluepixels P_(r), P_(g), and P_(b).

The first and second pixel electrodes 221 and 22 may function as anodes,and the first and second opposite electrodes 224 a and 224 b mayfunction as cathodes. Alternatively, the first and second pixelelectrodes 221 and 222 may function as cathodes, and the first andsecond opposite electrodes 224 a and 224 b may function as anodes.

The first pixel electrode 221 is formed in each of the pixels in a sizesubstantially corresponding to the first emission area PA1. In addition,the second pixel electrode 222 is formed in each of the pixels in a sizesubstantially corresponding to the second emission area PA2.

The first and second opposite electrodes 224 a and 224 b may be appliedby a common voltage with respect to entire pixels in the organicemission unit 21.

At least one of the passivation layer 218, the gate insulating layer213, the interlayer dielectric 215, and the pixel defining layer 219 maybe formed at least partially of a transparent insulating material. Here,the light transmittance of the substrate 1 may be less than or equal tothe entire light transmittance of the above insulating layers (213, 215,218 and 219).

FIG. 7A is a detailed schematic cross-sectional view of the firstemission area PA1, and FIG. 7B is a detailed schematic cross-sectionalview of the second emission area PA2.

The first pixel electrode 221 may be at least partially reflective, andthe first opposite electrode 224 a may be at least partiallytransmissive and at least partially reflective. In this embodiment, thefirst emission area PA1 is a top emission type which displays imagestoward the first opposite electrode 224 a.

In one embodiment, when the first pixel electrode 221 is reflective, thepixel circuit unit PC disposed under the first pixel electrode 221 isblocked by the first pixel electrode 221. Accordingly, as shown in FIG.6, the user may not see patterns of the first thin film transistor TR1,the capacitor Cst, and the second thin film transistor TR2 under thefirst pixel electrode 221 from an upper outer portion of the firstopposite electrode 224 a.

In this embodiment, since the first pixel electrode 221 is thereflective electrode, the light is only emitted toward the observer(user), and thus, loss of light to the opposite side of the observer maybe reduced. In addition, since the first pixel electrode 221 blocks thevarious patterns of the pixel circuit as described above, the user maysee substantially clear transmission images.

The second pixel electrode 222 may be at least partially transparent andthe second opposite electrode 224 b may be at least partiallyreflective. In this embodiment, the second emission area PA2 is a bottomemission type which displays images toward the second pixel electrode222.

The second pixel electrode 222 may be formed substantiallysimultaneously when the first pixel electrode 221 is formed. Forexample, the transparent metal oxide layer of the first pixel electrode221 except for the reflective layer may be patterned to extend to thesecond pixel electrode 222.

The first pixel electrode 221 may include a first transparent conductivelayer 221 a, a reflective layer 221 b, and a second transparentconductive layer 221 c. The first and second transparent conductivelayers 221 a and 221 c may be formed at least partially of indium tinoxide (ITO), indium zinc oxide (IZO), ZnO, or In₂O₃ having a high workfunction. The reflective layer 221 b may be formed at least partially ofAg, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Yb, or a compoundthereof.

The organic layer 223 including a first functional layer 223 a, anemission layer 223 b, and a second functional layer 223 c is formed onthe first pixel electrode 221, and the first opposite electrode 224 a isformed on the organic layer 223.

The first functional layer 223 a may include the HIL and the HTL, andthe second functional layer 223 c may include the EIL and the ETL.

The first opposite electrode 224 a may be formed at least partially ofmetal having a low work function, for example, Ag, Mg, Al, Pt, Pd, Au,Ni, Nd, Ir, Cr, Li, Ca, Yb, or an alloy thereof. The first oppositeelectrode 224 a may be formed as a thin film so as to increase the lighttransmittance, for example, the first opposite electrode 224 a may beformed to a thickness t2 of about 100 Å to about 300 Å.

At this time, the distance t1 between a surface of the reflective layer221 b and the first opposite electrode 224 a may be adjusted to generatean optical resonance with respect to the wavelength of the light emittedfrom the emission layer 223 b. Therefore, the distance t1 may varydepending on the pixels, that is, red, green, and blue pixels. In orderto adjust the distance t1 for generating the optical resonance, thefirst functional layer 223 a and/or the second functional layer 223 cmay further include an auxiliary layer for varying the thickness of theorganic layer according to the color of the pixel.

The first emission area PA1 having the above structure is the topemission type area for displaying images toward the opposite electrode224, and the light extracting efficiency may be maximized by adjustingthe distance t1 for generating the optical resonance.

In one embodiment, the second pixel electrode 222 is formed at leastpartially of a transparent conductive material without including areflective layer, as described above. Therefore, at least one of thefirst and second transparent conductive layers 221 a and 221 c of thefirst pixel electrode 221 may extend to form the second pixel electrode222.

The organic layer 223 including the first functional layer 223 a, theemission layer 223 b, and the second functional layer 223 c is formed onthe second pixel electrode 222, and the second opposite electrode 224 bis formed on the organic layer 223.

In the second emission area PA2, since there is no reflective layer inthe second pixel electrode 222, there is no need to adjust the opticalresonant distance. In addition, since the second emission area PA2 isthe bottom emission type which displays images toward the second pixelelectrode 222, and the thickness t3 of the second opposite electrode 224b may be greater than the thickness t2 of the first opposite electrode224 a. Accordingly, the second opposite electrode 224 b may reflect thelight emitted from the emission layer 223 b more than the first oppositeelectrode 224 a does. That is, since the thickness t3 of the secondopposite electrode 224 b is greater than the thickness t2 of the firstopposite electrode 224 a, the light reflectivity of the second oppositeelectrode 224 b is greater than that of the first opposite electrode 224a.

However, the second opposite electrode 224 b may be formed to transmitthe light to a predetermined extent, and may be formed not to beexcessively thick.

In addition, if the first and second opposite electrodes 224 a and 224 bare formed of a transparent material having a work function of cathode,the first and second opposite electrodes 224 a and 224 b may be formedto have substantially the same thickness as each other. In this case,the first opposite electrode 224 a further includes a thinsemi-transmission metal layer in order to improve the resonant effect.

In one embodiment, the second opposite electrode 224 b is formed on onlypart of the transmission area TA as shown in FIGS. 5 and 6, and thus,the user may see the external images through the transmission area TAwithout any obstacle.

In one embodiment, the second emission area PA2 is formed on only partof the transmission area TA, and accordingly, the external lighttransmittance of the transmission area TA does not degrade much.

In addition, as shown in FIG. 6, a first transmission window 230 isformed in the second opposite electrode 224 b. The first transmissionwindow 230 may be a hole formed in the second opposite window 224 b. Inaddition, since the first transmission window 230 is located on thetransmission area TA, degradation of the light transmittance of thetransmission area TA may be minimized or substantially prevented evenwhen the second opposite electrode 224 b that is thicker than the firstopposite electrode 224 a is located on the transmission area TA.

Furthermore, the user may see clear images through the first emissionarea TA1, and may see external images transmitted through thetransmission area TA. In addition, a person located opposite to the usermay see the images through the second emission area PA2, although imagequality may be lower than the images displayed through the firstemission area PA1. Accordingly, the organic light emitting display mayrealize a dual-emission display and a transparent display, at the sametime.

As described above, when the second opposite electrode 224 b is formedof the transparent material having the work function of the cathode,there is no need to form an additional transmission window in the secondopposite electrode 224 b as shown in FIG. 8.

In one embodiment, in order to improve the light transmittance of thetransmission area TA and to substantially prevent generation of opticalinterference caused due to the multi-transparent insulating layers inthe transmission area TA and degradation of color purity and colorchange caused by the optical interference, a second transmission window231 (FIG. 9) is formed in some insulating layers among the insulatinglayers corresponding to the transmission area TA.

In the present embodiment, in order to improve the external lighttransmittance of the transmission area TA, the area of the transmissionarea TA is increased, or the light transmittance of the material formingthe transmission area TA is increased. However, there is a limitation inincreasing the area of the transmission area TA due to the pixel circuitunit PC. In addition, there is a limitation in increasing the lighttransmittance of the material forming the transmission area due todifficulty in developing the materials.

In one embodiment, the second transmission window 231 is formed in atleast some of the insulating layers located on the portionscorresponding to the transmission area TA.

In FIG. 9, the second transmission window 231 is formed in thepassivation layer 218 that covers the pixel circuit unit PC. In oneembodiment, as shown in FIG. 9, the second transmission window 231 isformed in the passivation layer 218. However, holes connecting to thesecond transmission window 231 may be further formed in at least one ofthe interlayer dielectric 215, the gate insulating layer 213, and thebuffer layer 211 so as to improve the light transmittance through thesecond transmission window 231. The second transmission window 231 isformed as large as possible within a range of not interfering with thescan lines S, the data lines D, and the Vdd lines V.

In addition, the second transmission window 231 may be greater than thefirst transmission window 230 formed on the second opposite electrode224 b so as to improve the light transmittance of the transmission areaTA.

Here, at least part of the second pixel electrode 222 may be disposed toextend to and/or contact the second transmission window 231.

FIG. 10A is a schematic cross-sectional view of a first emission areaPA1 according to another embodiment, and FIG. 10B is a schematiccross-sectional view of a second emission area PA2 according to anotherembodiment.

According to the present embodiment, a first pixel electrode 221′ and asecond pixel electrode 222′ may respectively include reflective layers221 b′ and 222 b′, third transparent conductive layers 221 a′ and 222a′, and fourth transparent conductive layers 221 c′ and 222 c′.

In one embodiment, the thickness t4 of the reflective layer 221 b′ inthe first pixel electrode 221′ and the thickness t5 of the reflectivelayer 222 b′ in the second pixel electrode 222′ are substantially thesame as each other, and at this time, the thickness t4 and t5 may beless than the thickness of the reflective layer 221 b shown in FIG. 7Aaccording to the previous embodiment. The thickness t4 of the reflectivelayer 221 b′ in the first pixel electrode 221′ and the thickness t5 ofthe reflective layer 222 b′ may be about 100 Å to about 300 Å.

The first opposite electrode 224 a and a second opposite electrode 224b′ may be half-transmission and half-reflective electrodes. In oneembodiment, the thickness t2 of the first opposite electrode 224 a andthe thickness t3′ of the second opposite electrode 224 b′ aresubstantially the same as each other, that is, about 100 Å to about 300Å.

According to the present embodiment, both of the first and secondemission areas PA1 and PA2 are formed as the top-emission type; however,the thin reflective layers 221 b′ and 222 b′ are formed in the first andsecond pixel electrodes 221′ and 222′ so that the first and secondemission areas PA1 and PA2 substantially perform as the dual-emissiontype.

Here, as shown in FIGS. 3 and 4, the pixel circuit unit PC is located onthe first emission area PA1, and thus, less light is emitted as thebottom emission and more light is emitted as the top emission among thelight emitted from the emission layer 223 b.

Since the second emission area PA2 is located on the transmission areaTA, the images may be displayed on both surfaces.

The first and second transmission windows 230 and 231 illustrated inFIGS. 6 and 9 may be applied to the present embodiment.

FIG. 11 is a plan view of an organic emission unit according to anotherembodiment, in which one second transmission window 231′ is formedthroughout the red, green, and blue pixels P_(r), P_(g), and P_(b).Although not shown in FIG. 11, the first transmission window may beformed in the second opposite electrode.

In this case, the area of the transmission window 231′ increases in onepixel including the red, green, and blue pixels P_(r), P_(g), and P_(b),and thus, the light transmittance of the organic emission unit 21 may beincreased.

The structures illustrated in FIGS. 3 through 10 b may be applied to theorganic emission unit of FIG. 11 according to the present embodiment.

According to at least one of the disclosed embodiments, a transparentorganic light emitting display may be realized by increasing an externallight transmittance, and at the same time, a dual-emission image displaymay be realized.

In addition, a transparent organic light emitting display may preventdistortion of a transmission image by restraining scatter of thetransmitting light.

While the disclosed embodiments have been particularly shown anddescribed with reference to accompanying embodiments thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the following claims.

What is claimed is:
 1. An organic light emitting display comprising: a substrate; a plurality of pixels formed on the substrate, wherein each of the pixels comprises i) a first light emission area, ii) a second light emission area iii) at least one light transmission area, and iv) a pixel circuit unit, and wherein at least part of the second emission area overlaps with the light transmission area; a transmission window formed in the light transmission area; a first pixel electrode formed on the first light emission area and electrically connected to the pixel circuit unit, wherein the first pixel electrode is at least partially reflective; a second pixel electrode formed on the second light emission area and electrically connected to the first pixel electrode, wherein the second pixel electrode is at least partially transmissive; an opposite electrode substantially directly below or above the first pixel electrode and the second pixel electrode; and an organic emission layer formed between the first pixel electrode and the first opposite electrode and between the second pixel electrode and the second opposite electrode, wherein the transmission window is not overlapped with the second pixel electrode and the opposite electrode.
 2. The organic light emitting display of claim 1, wherein the first and second pixel electrode contact each other.
 3. The organic light emitting display of claim 1, wherein the first pixel electrode is thicker than the second pixel electrode.
 4. The organic light emitting display of claim 1, wherein the second pixel electrode is formed of a partially transmissive material and a partially reflective material.
 5. The organic light emitting display of claim 1, wherein the pixel circuit unit is formed substantially directly below or above the first pixel electrode and is not formed in the light transmission area.
 6. The organic light emitting display of claim 1, wherein the second pixel electrode is closer to the light transmission area than the first pixel electrode.
 7. The organic light emitting display of claim 1, further comprising at least one insulating layer contacting the pixel circuit unit, wherein the transmission window exposes an insulating layer of the at least one insulating layer.
 8. The organic light emitting display of claim 1, wherein the transmission window is formed in a pixel defining layer.
 9. The organic light emitting display of claim 1, comprising a second transmission window formed in a passivation layer and formed between the first and second pixel electrodes.
 10. The organic light emitting display of claim 1, further comprising a passivation layer covering the pixel circuit unit, wherein further comprising a second transmission window formed as a hole in a passivation layer.
 11. The organic light emitting display of claim 10, wherein the second transmission window is greater than the first transmission window.
 12. The organic light emitting display of claim 1, further comprising a plurality of insulating layers formed over the substrate, and further comprising a second transmission window formed on an insulating layer of the plurality of insulating layers. 